To improve convenience when operating a vehicle, a portable device for operating the vehicle is used in an electronic key system. Japanese Laid-Open Patent Publication No. 2013-19224 describes a portable device including electronic components such as a circuit board and a battery. The feature of the portable device is in how the circuit board is accommodated in the portable device.
In the portable device of the above publication, the circuit board, which includes a surface on which circuit elements are mounted, is held between a protection cover and a battery holder. Thus, the entire circuit board is concealed by the protection cover and the battery holder. The protection cover includes projections, each including an engagement hook. The engagement hook of the protection cover is snap-fitted to a corresponding groove located in an outer wall of the battery holder. This couples the protection cover to the battery holder. The engagement hook extends from the corresponding projection of the protection cover toward the circuit board. The protection cover includes a guard plate at the rear of each projection (engagement hook). The guard plate covers the projection so that the engagement hook cannot be seen from the exterior when the protection cover is coupled to the battery holder.
Many circuit elements and wires that connect the circuit elements are mounted on the circuit board. Thus, the circuit board needs sufficient space for a circuit area where the circuit elements and the wires are mounted. To miniaturize the protection cover and the battery holder, each guard plate will have to be located at a further inner position on the protection cover. In such a case, the projection (particularly, engagement hook) of the protection cover will partially occupy and reduce the size of the circuit area for the circuit elements and the wires. To enlarge the circuit area for the circuit elements and the wires, each projection (engagement hook) and the corresponding guard plate will have to be located at a further outer position on the protection cover. This will enlarge the protection cover and the battery holder. Therefore, there is a trade-off between the miniaturization of the protection cover and the battery holder and the enlargement of the circuit area for the circuit elements and the wires.